Exemplary embodiments of the present invention relate to a compressor, a method for operating a compressor and a fuel cell device.
Fast-rotating work machines, in particular compressors, which are driven electrically, are equipped with ball bearings or with air bearings.
Conventional air bearings, in particular formed as foil air bearings or “Foil Air Bearing”, in principle generate higher friction losses than ball bearings, wherein a large part of the losses is mainly generated by axial bearings.
U.S. Patent Application Publication No. US 2007/0069597 A1 discloses a compressor with a housing and a moving part, wherein the housing has an air guide section and a bearing section, and the moving part has a compressor wheel and a shaft connected to the compressor wheel in a pivot-proof manner. The shaft is mounted in a pivoted manner in the bearing section, and the compressor wheel is received in a first chamber in the air guide section in a pivoted manner. The shaft can be driven with the help of an electric motor. At least one radial bearing and an axial bearing are provided for the mounting of the shaft. The radial bearings are in the form of conventional air bearings. The axial bearing has magnetic bearings and air bearings. One problem with this arrangement is that magnets of the magnetic bearings are formed at rotatable sections of the magnetic bearing and do not have a secured fixing with the expected circumference speeds and high centrifugal forces.
Exemplary embodiments of the present invention reduce the friction losses generated during the operation of an electrically supported compressor while considering a secured operation.
According to one aspect of the invention, the axial bearing of the compressor comprises at least a first bearing and a second bearing, wherein the first bearing is formed in the region of the compressor wheel and the second bearing in the region of an end of the moving part facing away from the compressor wheel. A reduction of the friction losses is advantageously achieved by division of the axial bearing and the corresponding arrangement of the first bearing and the second bearing.
One bearing of the axial bearing can be a magnetic bearing and the other bearing of the axial bearing is a point bearing.
For increasing a drive performance of the compressor, a turbine is assigned to the compressor in such a manner that the housing additionally comprises an exhaust gas guide section and the moving part additionally a turbine wheel of the turbine, wherein the turbine wheel is received rotatably in a second chamber of the exhaust gas guide section and the turbine wheel is connected in a pivot-proof manner at an end of the shaft positioned facing away from the compressor wheel.
The magnetic bearing can comprise a holding device, which is formed in the entry channel near the compressor wheel.
The magnetic bearing can comprise at least two magnets, wherein a first magnet is fixed in the holding device and a second magnet in a hub of the compressor wheel at an end of the compressor wheel positioned facing the entry channel.
The magnetic bearing can comprise at least two magnets, which are arranged in such a manner that the same poles of the magnets are arranged facing each other.
The magnetic bearing can have at least two magnets, wherein at least one magnet is formed in the shape of a cylinder.
The point bearing comprises, in particular, a holding device positioned in the exit channel in the region of the turbine wheel.
The point bearing can comprise at least two balls, wherein a first ball is fixed in the holding device and a second ball in a hub of the turbine wheel at an end of the turbine wheel positioned facing the exit channel.
The point bearing can comprise two balls, which are formed of different materials.
In particular one ball, in particular the second ball, is formed of a hardened material, in particular steel, and the other ball, in particular the first ball, of a ceramic material.
At least one ball, in particular the first ball, of the point bearing can be moved axially, wherein the axial movement is ensured by a thread.
The axially movable ball can be fixed at a cylinder, which is received movably in the holding device of the point bearing by means of the thread.
At least one magnet, in particular the first magnet, can be formed in an annular manner. The other magnet, in particular the second magnet, can be arranged in the wheel back of the compressor wheel, so that the magnets repel.
The holding device of the magnetic bearing can be formed by a first radial bearing.
Both bearings of the axial bearing can be formed as magnetic bearing.
The shaft can be positioned axially contactless by the axial bearing, in particular in dependence on the design of the bearings, at least from a certain speed of the moving part.
The bearings can both be formed as magnetic bearings and the shaft is positioned permanently in a contactless manner.
The bearings of the axial bearing can be arranged on an axis. In particular, the magnets of the at least one magnetic bearing are arranged on this axis. Preferably, the magnets of the magnetic bearing and the balls of the point bearing are arranged on the axis with an arrangement of the axial bearing with a magnet and a point bearing.
With a method according to the invention for operating an exhaust gas turbocharger with a housing and a moving part, wherein the housing has an air guide section, an exhaust guide section and a bearing section, and the moving part a compressor wheel, a turbine wheel and a shaft connecting the compressor wheel with the turbine wheel in a pivot-proof manner, the shaft is mounted rotatably in the bearing section. The compressor wheel is received in a first chamber of the air guide section and the turbine wheel is received in a second chamber of the exhaust guide section in a rotatable manner, wherein the shaft is driven with the help of an electric motor, and for the mounting of the shaft in the bearing section, at least one radial bearing and an axial bearing is formed, wherein the axial bearing has at least one magnetic bearing. The axial bearing comprises at least one first bearing and a second bearing, wherein the first bearing is formed in the region of the compressor wheel and the second bearing in the region of the turbine wheel.
In particular, with standstill and low speeds of the moving part, the first ball and the second ball of the point bearing of the axial bearing contact. From a certain speed of the moving part, from which air is taken in by the compressor wheel and is compressed, the charge pressure in a spiral channel is also formed at a wheel back of the compressor wheel. An axial force on the compressor wheel results thereby, wherein the compressor wheel and therewith the entire moving part is moved axially in the direction of the first entry channel. Due to this axial movement, the contact of the first ball and of the second ball is cancelled. With the help of the magnetic bearing and its magnets positioned in a repelling manner, a force balance results at the moving part with regard to the axial forces, so that the shaft of the moving part is positioned in an axially contactless manner and thus also in a frictionless manner.
A further aspect of the invention relates to a fuel cell device, in particular a mobile fuel cell device for use in a vehicle, in particular a motor vehicle, which comprises an exhaust gas turbocharger according to the invention or an advantageous embodiment thereof. The exhaust gas turbocharger is in particular used there for supplying oxidation means, such as oxygen of the oxygen-containing gas, to the fuel cell stack of the fuel cell device and/or for discharging the exhaust gas discharged by the fuel cell stack.
Advantageous embodiments of the exhaust gas turbocharger according to the invention are to be viewed as advantageous embodiments of the fuel cell device and as advantageous embodiments of the method according to the invention for operating the exhaust gas turbocharger.